A construction machine including hydraulic actuators which drive drive portions such as a boom and an arm with motive power from a hydraulic pump driven by an engine has been heretofore used as this type of construction machine such as hydraulic excavator. However, in recent years, a hybrid type construction machine aimed at improvement of fuel efficiency of an engine, reduction of noise level, and reduction of exhaust gas, etc. has been developed and implemented practically. Specifically, this hybrid type construction machine has a generator motor which is used for assisting the hydraulic pump and which can generate electric power by the engine, and an electric storage device which can supply electric power for driving the generator motor and which can be charged with electric power generated by the generator motor.
In addition, for example, a hybrid working machine described in Patent Literature 1 has been known as a background-art technique in the technical field. Specifically, the working machine described in Patent Literature 1 includes an engine, a hydraulic pump which is driven by the engine, hydraulic actuators which are operated by motive power from the hydraulic pump, and a generator motor which assists motive power to the hydraulic pump. In addition, the working machine includes an electric storage unit which exchanges electric energy with the generator motor. The working machine is configured to limit a motoring torque value of the generator motor in accordance with the residual power level of the electric storage unit. In the Patent Literature 1, configuration is made to suppress accelerative increase of power consumption caused by increase of a current and suppress remarkable decrease of the residual power level caused by the increase of power consumption when a predetermined assist operation is performed in a state in which the residual power level is low.